[llvm] [SDAG] Preserve InBounds in DAGCombines (PR #165424)

[Fabian Ritter via llvm-commits]

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@@ -2715,6 +2715,12 @@ SDValue DAGCombiner::visitPTRADD(SDNode *N) {
           (N->getFlags() & N0->getFlags()) & SDNodeFlags::NoUnsignedWrap;
       SDValue Add = DAG.getNode(ISD::ADD, DL, IntVT, {Y, Z}, Flags);
       AddToWorklist(Add.getNode());
+      // We can't set InBounds even if both original ptradds were InBounds and
+      // NUW: SDAG usually represents pointers as integers, therefore, the
+      // matched pattern behaves as if it had implicit casts:
+      //   (ptradd inbounds (inttoptr (ptrtoint (ptradd inbounds x, y))), z)
+      // The outer inbounds ptradd might therefore rely on a provenance that x
+      // does not have.
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ritter-x2a wrote:

I'd leave that to a CHERI-upstreaming-related patch that should (among other things) remove this assert in the lines above this change to enable PTRADD combines for CHERI:
```
  assert(PtrVT == IntVT &&
         "PTRADD with different operand types is not supported");
```

https://github.com/llvm/llvm-project/pull/165424